Recent years have seen a strong emphasis on efficient use of the world's limited resources, particularly in the energy or electric power field. The limited supply of fossil fuels has especially aggravated the need for more efficient energy usage. At the same time, factors such as modern building design, high seasonal temperatures (depending on location), poorer outdoor air quality and increased demand for frozen and perishable foods have combined to produce an ever-increasing demand for large, expensive-to-operate and frequently inefficient air conditioning and refrigerating equipment.
While the demand for such equipment has had the beneficial effect of strengthening the various manufacturers thereof, the intensive use of the equipment has placed heavy burdens on the power production capacities of public utilities in many localities. Such air conditioning and refrigerating systems consume prodigious amounts of power in doing their work and, by their design, reject very large amounts of energy, usually to the atmosphere, to cool and condense their hot refrigerant gas. In such systems, the flowing refrigerant liquid is expanded, thereby lowering its temperature. Heat is then absorbed from the area to be cooled, thereby lowering the area's temperature and converting the refrigerant back to a gas. After this, the refrigerant gas is compressed to restore it to high pressure. To remove the heat absorbed from the area to be cooled, most conventional prior art systems pass the refrigerant gas through a condenser where the refrigerant gas is cooled under essentially constant pressure usually until it reaches a state close to a saturated liquid or perhaps to a state with a slight degree of subcooling. The heat removed is normally dissipated into the surrounding air at the location of the condenser. This represents a tremendous waste in energy over a period of time. Could this energy be effectively harnessed, substantial economies would result.
One approach to this problem is shown in U.S. Pat. No. 3,922,876. In this device, the refrigerant gas is passed through one side of a heat exchanger located upstream of the condenser to reject heat to water flowing intermittently through the other side of the heat exchanger. To control condensation in the heat exchanger, the patented device includes a temperature sensitive valve which stops water flow when the water inlet temperature drops to the temperature at which an unacceptable portion of the refrigerant gas would condense. Thus, when connected to a hot water heating system, the patented device will be inoperative for water inlet temperatures below about the 100.degree. F. to 140.degree. F. range where most commercially available refrigerants will condense completely. Until the water inlet temperature is high enough, the conventional hot water heater must reheat the water. This results in rather long recovery times and very little saving due to heat reclamation, particularly during high demand periods. Unfortunately, the bulk of the heat contained in the refrigerant gas will be lost while waiting for the inlet temperature of the water to rise, leading to reduced efficiency of reclaiming heat from the refrigerant.
Various other prior art systems have included some sort of supplemental heat exchanger for transmitting heat from the refrigerant to a hot water system. U.S. Pat. Nos. 2,516,093, 2,751,761, 3,188,829, 3,301,002, 3,308,877, 3,366,166, 3,563,304, 3,916,638, and 3,926,008 show typical prior art refrigerating approaches including means for heating water by absorbing heat from the refrigerant using a supplemental heat exchanger at a location upstream of the conventional condenser. In these cases, however, the teachings of the patents to those skilled in the art are rather clear that the supplemental heat exchanger, or pre-cooler for the refrigerant gas, as it is sometimes called, is to be placed in a large volume of water relative to the volume of refrigerant flowing through the heat exchanger at a given point in time. Because of this, at least until the water has been heated substantially beyond the usual temperature range for municipal water of 35.degree. to 55.degree. F., the refrigerant would be expected to condense completely to a saturated liquid in the pre-cooler heat exchanger, leaving for the conventional condenser the task of subcooling the liquid refrigerant and for the compressor the added work of circulating liquid through a greater part of the system.
In systems where the compressor flow rates; piping lengths; relative height of compressor and condenser; presence of low points; flow velocity reducing elements such as elbows and bends in refrigerant tubing; system insulation; number of valves and related factors can be adjusted at the time of system installation, the presence of such large amounts of liquid refrigerant upstream of the conventional condenser may be acceptable. However, where it is desired to modify an existing installation to include a supplemental heat exchanger for heating a medium such as water, the system parameters such as those just listed are not easily, economically changed in most instances.
Since it is desirable to modify an existing system as little as possible when providing a supplemental heat exchanger for hot water, the amount of liquid refrigerant in the discharge from the supplemental exchanger is of considerable importance. An excess of liquid can lead to collection of puddles of mixtures of liquid refrigerant and the lubricating oil usually carried with the refrigerant gas, at low points in the refrigeration system tubing leading to the conventional condenser, or even in the supplemental heat exchanger itself. If these puddles form slugs which block the refrigeration system tubing, the tubing upstream becomes over-pressurized as the compressor keeps on pumping in more gas; and the tubing downstream becomes starved as the compressor keeps on pumping away its refrigerant. The refrigeration capacity of the system deteriorates until the puddle or slug of liquid begins to move rapidly through the system under the influence of the higher upstream pressure. This movement continues with "rifle shot" speed until another low point is reached, following which the process repeats itself. Should a slug reach the compressor or another vital component, serious damage may result. Such slugs have been known to rupture the tubing. Or, the slugs or other large amount of liquid entering the conventional condenser may first flood its inlet plenum and then the condenser itself, giving rise to poor performance. Thus, following such prior art teachings concerning refrigerating and air conditioning systems, supplemental heat exchangers for heating a medium such as water would not lead to satisfactory results when modifying an existing system.